In a typical lost foam casting process, a foam mold pattern is placed within a mold flask, wherein the foam pattern includes a foam riser that extends from the foam pattern toward the top of the flask. Sand from a batch hopper located above the flask is poured into the flask around the foam pattern. As the sand fills the flask, the sand compacts about the foam pattern through the use of vibration. After the flask has been adequately filled with sand, which preferably corresponds to a level equal to the top of the riser, molten metal is poured onto the riser to engage the foam pattern, and the molten metal vaporizes the foam riser and pattern. Thus, the molten metal replaces the foam pattern. The metal is cooled until the casting is solidified, at which time the casting and sand are removed from the flask.
The distribution of sand into the flask in many prior art embodiments is controlled through monitoring the period of time during which the sand gate is in an open position. Using such a method, the user estimates the length of time that is required to distribute the desired amount of sand around a particular foam pattern according to the complexity of the design of the pattern, and the user opens the sand gate for this proper period of time. As a result, the accurate and desired distribution of sand using this method may not occur due to the varying conditions of the types of sand used and the flowability related thereto. For example, if the sand does not flow well from the batch hopper, then the sand received in the flask will be too low to fill the cavities of the foam pattern. This problem is illustrated in FIG. 1A wherein sand 2 does not engage the cavity 6 within the foam pattern 4. However, if the sand overflows into the flask, there is too much overburden at the entrance of the cavity 6 and the sand will not be fluidized at the entrance of the cavity 6 of the pattern. As a result, the sand will not be able to fully fill the cavities of the pattern. This problem is illustrated in FIG. 1B wherein sand 2 substantially overburdens the foam pattern 4 and does not fully fill the cavity 6. Additionally, if the user desired to deposit multiple different layers of sand from the batch hopper using the timing method, each independent and different layer of sand would be subject to inaccuracies caused by the variations in the flow rates of sand, which will also provide a cumulative effect of providing multiple inaccurate layers within the flask. However, looking at FIG. 1C, when the proper depth of sand 2 is distributed into the flask having the desired flow rate, there will be only a slight overburden of the sand 2 on the pattern 4, which will promote the rapid and complete filling of the cavity of the pattern 4.
Accordingly, what is needed is a sand level sensing and distribution apparatus to provide an accurate control of the depth and flow rate of the layers of sand that are deposited into the flask such that the sand in the flask will flow to a proper height around the mold positioned in the flask to substantially surround and engage a foam pattern.